JPH0519262A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display element which has ferroelectric liquid crystal molecules in a uniform state, is wide in the pulse width to drive the element, i.e., is increased in driving margin, is wide in a well switching region and has a high response speed. CONSTITUTION:This liquid crystal display element is constituted by disposing two sheets of electrode substrates 10, each formed by providing transparent electrodes 12 on a substrate 11 and providing an oriented film 14 subjected to a rubbing treatment on the surface of the transparent electrodes 12, in such a manner that the oriented films 14 exist on the inner side and sealing the ferroelectric liquid crystal compn. 30 into the cell constituted in the above- mentioned manner. The liquid crystal molecules of such liquid crystal display element are oriented in the uniform state and the rubbing directions A, B of the oriented films 14 of two sheets of the electrode substrates 10 intersect at the angle within a 2 to 30 deg. range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display elements used in clocks, computers, word processors, etc.
As its basic structure, it is usual that two transparent electrode substrates each having an alignment film provided on a transparent electrode are arranged with the alignment film inside, and a liquid crystal is sealed between them. The transparent electrode of such a liquid crystal display device is generally formed on the substrate in the form of a display pattern such as a stripe pattern or a grid pattern, and the alignment film is formed on the transparent electrode and the exposed substrate (other than the display pattern). Is provided by coating or vapor deposition. The two transparent electrode substrates are respectively arranged with the alignment film inside, and a ferroelectric liquid crystal is sealed between them to manufacture a liquid crystal display element. Therefore, the enclosed liquid crystal is generally in contact with only the alignment film. In general, the alignment film is provided because it is necessary to align the liquid crystals in a certain direction, that is, to align the liquid crystals, and thereby the liquid crystal molecules are aligned.

The mainstream of such a liquid crystal display device is a display in a twisted nematic (TN) mode in which a nematic liquid crystal has a twisted structure. However, this TN type liquid crystal display element has a drawback that the response speed is slow and the limit is 20 milliseconds under the present circumstances, which is a big problem when it is used for a television panel or the like which requires high speed response. Is becoming

On the other hand, recently, a ferroelectric liquid crystal having a high-speed response has been expected and studied as a new field of display.

Ferroelectric liquid crystals not only respond rapidly to changes in the electric field, but also take one of a first optical stable state and a second optical stable state in response to an applied electric field. In addition, it also has a property of maintaining its state when no voltage is applied, that is, a memory property (also called bistability). Therefore, in the liquid crystal display device using the ferroelectric liquid crystal, it is sufficient to apply the pulse voltage only when switching between the two states, so that the power supply and the electronic circuit for maintaining the optical state as in the past are not necessary. Therefore, the power consumption is reduced as compared with the conventional liquid crystal display element. That is, it can be said that the liquid crystal display element using the ferroelectric liquid crystal is a liquid crystal display element having a simple structure and realizing high-speed response.

In order to switch the above two optical stable states at high speed and surely and to improve the memory property, it is necessary to orient the ferroelectric liquid crystal uniformly. In order to align the ferroelectric liquid crystal, it is general to use an organic thin film as the alignment film, and a film obtained by rubbing the organic thin film, or a film obtained by obliquely depositing an inorganic oxide as the alignment film.

A rubbing polyimide film is generally used as the alignment film. The rubbing polyimide film is obtained by using, for example, polyamic acid which is a polyimide precursor, pyridine, N-methyl-2-pyrrolidone, dioxane, and TH.
A solution prepared by dissolving F, a glycol derivative or the like in an appropriate solvent is prepared, and the solution is applied onto a transparent electrode by spin coating or the like, dried at room temperature to 150 ° C., and the dried coating film is then dried at 200 to 300 ° C. It is formed by heating at a temperature to form a polyimide film, and then rubbing the polyimide film with synthetic fibers such as nylon, polyester, polyacrylonitrile, etc., and natural fibers such as cotton, wool, etc.

Ferroelectric liquid crystals generally have a spiral structure, but as the cell thickness is made thinner, the spiral structure disappears under the influence of the interface with the alignment film of the substrate, and the alignment state is stable in terms of energy. That is, the surface is stabilized.
The surface-stabilized state includes a uniform state in which molecules are evenly arranged and a twisted state in which molecules are twisted and arranged. Since the uniform state is approximately optically uniaxial, it becomes a dark field when the molecular axis direction is parallel to the polarizer or analyzer, and a bright field because of birefringence otherwise. That is, in the case of a uniform state, a dark field is obtained under crossed Nicols. On the other hand, in the twisted state, two states of different colors are observed without forming a dark field under crossed Nicols. Generally, it is said that as the cell thickness is reduced, the spiral state changes to a twisted state, and the twisted state changes to a uniform state. Whether to take a uniform state or a twisted state is determined by the mutual relationship between the ferroelectric liquid crystal composition and the cell thickness. The details are described in "Structure and Physical Properties of Ferroelectric Liquid Crystals" (published on May 25, 1990 by Corona Co., Ltd.) by Atsushi Fukuda and Hideo Takezoe.

Japanese Unexamined Patent Publication (Kokai) No. 62-151825 has two substrates having a uniaxial orientation axis, and at least two ferroelectric liquid crystals having a stable state are arranged between the two substrates. In a liquid crystal device having a cell structure, the two substrates have uniaxial alignment axes having different alignment regulating forces on surfaces in contact with the ferroelectric liquid crystal, and the uniaxial alignment axes intersect each other. Disclosed is a liquid crystal element. JP-A-62-1518
In the invention described in Japanese Patent No. 25, the uniaxial alignment axis that intersects at an angle that is opposite to the twist direction of the liquid crystal in the twisted state is used to eliminate the twisted alignment of the liquid crystal and The purpose is to obtain the maximum transmittance / light blocking ratio contrast. Further, JP-A-62-151825 does not describe a liquid crystal in a uniform state.

In such a liquid crystal display device using the twisted liquid crystal, a dark field cannot be obtained, and therefore, the contrast of the display image is small, defects are likely to occur, and the memory property is small. There is a point.

Therefore, the present inventors have studied a liquid crystal display device using a ferroelectric liquid crystal composition in a uniform state. However, the liquid crystal display device using the ferroelectric liquid crystal composition in a uniform state has a narrow drivable pulse width range and a low response speed, which is not satisfactory.

[0012]

DISCLOSURE OF THE INVENTION According to the present invention, while the excellent characteristics that the ferroelectric liquid crystal molecules are in a uniform state and good contrast is obtained, the drivable pulse width is wide, that is, Provided is a liquid crystal display device having a large response margin, a wide switching region, and a high response speed.

[0013]

According to the present invention, two electrode substrates each having a transparent electrode provided on a substrate and an alignment film rubbing-treated on the transparent electrode surface are provided with an alignment film inside. A liquid crystal display device in which a ferroelectric liquid crystal composition is enclosed in a cell arranged so that liquid crystal molecules are aligned in a uniform state, and an alignment film of two electrode substrates. The liquid crystal display device is characterized in that the rubbing directions of (1) and (2) intersect at an angle within the range of 2 to 30 degrees.

Preferred embodiments of the liquid crystal display device of the present invention are as follows. 1) The rubbing direction of the alignment films of the two electrode substrates is 3
The liquid crystal display device described above, wherein the liquid crystal display device intersects at an angle within a range of 15 degrees.

2) The liquid crystal display device as described above, wherein the rubbing directions of the alignment films of the two electrode substrates intersect each other with the central axis of the cone of liquid crystal molecules sandwiched therebetween.

The structure of the liquid crystal display device of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a main part of an example of the liquid crystal display element of the present invention.

In FIG. 1, the liquid crystal display element 1 is a transparent electrode in which a transparent electrode 12 is provided on a transparent substrate 11, an insulating film 13 is provided thereon, and an alignment film 14 is provided thereon. A transparent electrode substrate 20 in which a transparent electrode 22 is provided on a substrate 10 and a transparent substrate 21, an insulating film 23 is provided thereon, and an alignment film 24 is further provided thereon.
And a ferroelectric liquid crystal composition 30 is enclosed in a cell formed by arranging so that the alignment film 14 and the alignment film 24 face each other.

The transparent electrodes 12 and 22 are both formed in a stripe shape, and the transparent electrodes 12 and 22 are combined so that the stripe shapes are orthogonal to each other to form a liquid crystal display device capable of matrix display. Further, the transparent electrode may be formed in a stripe shape only on one side. An insulating film for preventing a short circuit between the upper and lower electrodes is provided, but the insulating film may not be provided in some cases.

Examples of the material of the transparent substrate include glass such as float glass having good smoothness, polyester such as polyethylene terephthalate and polybutylene terephthalate, epoxy resin, phenol resin, polyimide, polycarbonate, polysulfone, polyether sulfone,
Heat-resistant resins such as polyetherimide, acetylcellulose, polyamino acid ester, aromatic polyamide, vinyl polymers such as polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polyacrylamide, polyethylene, polypropylene, and fluorine-containing polymers such as polyvinylidene fluoride Examples thereof include a film or sheet of a polymer compound formed of a resin and a modified product thereof.

Examples of the material of the transparent electrode include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ) and ITO (indium tin oxide).
The transparent electrode is formed on the substrate in a stripe shape or a grid shape.

Examples of the material for the insulating film include metal oxides and metal nitrides.

As the alignment films 14 and 24, for example, a film of a polymer compound such as polyimide, polyvinyl alcohol, polyvinylidene fluoride and polyamide, a coating type alignment film such as a film of an organic silane compound, vacuum deposition, sputtering, etc. SiO ₂ , Si formed by vapor deposition of
Examples thereof include thin layers such as O and TiO ₂ . In particular, an organic coating type alignment film is preferable.

As an example of the coating type alignment film, a polyimide alignment film can be formed, for example, as follows.
First, polyamic acid which is a polyimide precursor is treated with pyridine, N-methyl-2-pyrrolidone, dioxane and TH.
A coating liquid for forming an alignment film dissolved in a suitable solvent such as F or a glycol derivative is prepared. The coating liquid may further contain other sub-components such as high molecular weight polymers and organometallic compounds for the purpose of increasing the adhesiveness to the substrate and adjusting the viscosity of the coating liquid. .. Coating liquid for forming alignment film
A transparent coater and an exposed substrate are coated with a spin coater or the like and dried at room temperature to 150 ° C. for 1 to 120 minutes (preferably 80 to 120 ° C. for 10 to 60 minutes), and then the coating film is formed at 150 to 150 ° C. A polyimide alignment film is formed by heat treatment at 300 ° C. for 0.5 to 3 hours. At this time, the drying process may be omitted depending on the case.

The thickness of the alignment films 14 and 24 varies depending on the type of liquid crystal used and the material of the alignment film, but is generally 1
It is 0 to 800 nm, preferably 20 to 50 nm.

The surface of the alignment film thus formed is
Rubbing is performed with synthetic fibers such as nylon, polyester, polyacrylonitrile, etc., and natural fibers such as cotton, wool, etc.

Further, a color filter, a black mask or the like may be provided between the substrate and the transparent electrode.

For the production of the substrate, the formation of the transparent electrode, the formation of the insulating film, the formation of the alignment film, the color filter, the black mask, etc., the techniques conventionally used for manufacturing the ferroelectric liquid crystal display device are applied. can do.

The liquid crystal display device of the present invention is characterized in that the enclosed liquid crystal is a ferroelectric liquid crystal composition and the liquid crystal molecules are aligned in a uniform state. That is, as described above, in a cell having a thin cell thickness, the ferroelectric liquid crystal has two kinds of surface-stabilized states, that is, a uniform state and a twisted state, but in the liquid crystal display element of the present invention, liquid crystal molecules are Oriented in a uniform state.

Since the condition of uniform alignment in the cell of the liquid crystal display device is determined by the interrelationship between the property of the ferroelectric liquid crystal composition and the cell structure, particularly the cell thickness, the characteristics of the ferroelectric liquid crystal composition. Cannot be specified independently. However, from among the ferroelectric liquid crystal compositions obtained by changing the types and compositions of various liquid crystal components and additive components other than liquid crystal, those which are in a uniform state when enclosed in a specific cell to be used ( For example, it can be easily determined by observing whether or not a dark field is displayed under crossed Nicols).

Therefore, each liquid crystal compound constituting the ferroelectric liquid crystal composition in the present invention is not particularly limited,
Chiral smectic C layer (SmC ^* ), H layer (Sm
H ^* ), I layer (SmI ^* ), J layer (SmJ ^* ), K layer (SmK
^* ), Any liquid crystal having a G layer (SmG ^* ) or an F layer (SmF ^* ) may be used.

The liquid crystal display device of the present invention has another feature in the rubbing treatment applied to the alignment film. That is, in the liquid crystal display device of the present invention, the rubbing direction of the alignment films of the two electrode substrates is 2 to 30 degrees, preferably 3 to 20.
Characterized in that they intersect at an angle in the range of 3 to 15 degrees, more preferably 3 to 15 degrees.

That is, in FIG. 2 showing a plan view of an example of the liquid crystal display device of the present invention, the rubbing direction A of the alignment film of the transparent electrode substrate 20 and the rubbing direction B of the alignment film of the transparent electrode substrate 10 are angled. It intersects at α and the angle α is 2 to 30
Is preferably in the range of 3 to 20 degrees, more preferably 3 to 15 degrees.

The rubbing directions A and B of the alignment films of the two electrode substrates preferably intersect each other with the central axis L of the cone of liquid crystal molecules (generally parallel to the side of the substrate) sandwiched therebetween.

As described above, also in the liquid crystal element disclosed in Japanese Patent Laid-Open No. 62-151825, the rubbing directions of the alignment films of the two electrode substrates intersect. However, in the liquid crystal element disclosed in Japanese Unexamined Patent Publication No. 62-151825, the liquid crystal is in a twisted state (in the example of the above publication, there are blue and yellow domains under crossed Nicols. Described), by using a uniaxial alignment axis intersecting at an angle opposite to the twist direction of the liquid crystal in the twisted state, the twisted alignment of the liquid crystal is eliminated,
The purpose is to obtain the maximum transmittance / light-shielding ratio contrast under crossed Nicols. Therefore, the present invention and the invention described in Japanese Patent Laid-Open No. 62-151825 are completely different from each other in the constitution (state of liquid crystal) and the purpose.

In the liquid crystal display device of the present invention, by intersecting the rubbing directions of the alignment films of the two electrode substrates, the driving margin is increased, the region for good switching is widened, and the response speed is increased. Although it is not always clear, the fact that the rubbing directions of the alignment films of the two electrode substrates are not parallel but intersect each other makes the response to the applied pulse of the liquid crystal stabilized in a uniform state,
It is speculated that it will give some kind of stimulation. In any case, as is clear from the results of Examples and Comparative Examples described later, the liquid crystal display element of the present invention is excellent in that the drive margin is increased, the region for good switching is widened, and the response speed is increased. Produce the effect.

[0036]

EXAMPLES Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to this embodiment.

[Example 1] Two glass plates (25 mm x
A transparent electrode (10 Ω / □) of indium-tin oxide (ITO) is stripe-shaped (width of electrode: 300 μm, gap between electrodes: 10 μ) on each of 20 mm × 1.1 mm.
m) to form a glass substrate with electrodes.

Polyimide forming coating solution (LQ1800)
4 g, N-methyl-2-pyrrolidone 5 g, diethylene glycol monoethyl ether 10 g and butoxy ethanol 10 g were mixed to prepare an alignment film coating liquid.

The glass substrate with the first electrode was attached to a spinner, and the above coating liquid for alignment film was applied onto the electrode surface while the glass substrate was kept stationary.
Spin at pm for 30 seconds to dry, then 295 ° C.
Was heat-treated for 1 hour to form an alignment film.

After cooling this to room temperature, the surface of the alignment film was rubbed with a nylon raised fabric under the conditions of 1400 rpm and 20 seconds × 3 times. The rubbing direction was inclined at 2 degrees with respect to a line parallel to one side of the glass substrate. That is,
The angle between the line L shown in FIG. 2 and the rubbing direction A (α /
2) was made twice.

An alignment film was formed on the electrode surface of the second electrode-attached glass substrate in the same manner as above, and subjected to rubbing treatment. The rubbing direction at this time is the angle at which the rubbing directions of the alignment films of the two glass substrates intersect when the first glass substrate and the electrode pattern are combined so that the alignment films face each other at right angles (that is, in FIG. The angle α) is set to 4 degrees. That is, the angle (α / 2) formed by the line L shown in FIG. 2 and the rubbing direction B is set to 2 degrees.

The two substrates with electrodes manufactured in this manner are superposed with a spacer (Makoto Kabushiki Kaisha, Ltd.) so that the alignment films face each other and the electrode patterns are orthogonal to each other. And a cell gap having a cell gap of 2 μm was produced by bonding with an epoxy adhesive. The angle at which the rubbing directions of the alignment films of two glass substrates with electrodes intersect (ie,
The angle α) shown in FIG. 2 was 4 degrees.

A ferroelectric liquid crystal composition having the composition and phase transition temperature shown in Table 1 was placed in this cell on a hot plate.
It was injected at 100 ° C. for 30 minutes and naturally cooled to room temperature to manufacture a liquid crystal display element.

[0044]

[Table 1]

With respect to the obtained liquid crystal display device, the pulse width range and the surface condition were measured by the methods described below. The results are shown in Table 2.

[Evaluation of Liquid Crystal Display Element] 1) Pulse width range A drive waveform of the 4-pulse method was applied to the liquid crystal display element at 35 ° C. (± 32 V, duty = 480, bias ratio = 1 /).
4) and then the microscope (Nikon OPTIPHOTO2-POL, objective lens M
The brightness of the bright frame (B) and the brightness of the dark frame (D) were measured using Plan 10) and a photodiode. The B / D ratio was measured while gradually increasing the pulse width. The maximum value of the B / D ratio (B / D) of the half of the _max B / D
When the ratio, the difference between the long pulse of the pulse width (PW _L) and short pulse-side pulse width _{(PW S) (| PW L} -PW S
|) Was determined as the pulse width range.

2) Planar observation under a crossed Nicols microscope, and a drive waveform of the 4-pulse method is applied, and under the condition that a bright frame and a dark frame are switched, good switching is performed for the entire display area of the liquid crystal display device. It evaluated by the ratio of the area | region which does. The symbols shown in Table 2 have the following meanings. ⊚: 90% or more of good switching area ◯: 80% or more and less than 90% of good switching area ×: less than 50% of good switching area

[Example 2] A cell in which the rubbing direction of the alignment film is changed and the angle at which the rubbing directions of the alignment films of the two glass substrates with electrodes intersect (that is, the angle α shown in FIG. 2) is 10 degrees. A liquid crystal display device was manufactured in the same manner as in Example 1 except for manufacturing.

About the obtained liquid crystal display element, Example 1
The pulse width range and surface condition were measured by the same method as in. The results are shown in Table 2.

Example 3 A cell in which the rubbing direction of the alignment film is changed and the angle at which the rubbing directions of the alignment films of the two glass substrates with electrodes intersect (that is, the angle α shown in FIG. 2) is 20 degrees. A liquid crystal display device was manufactured in the same manner as in Example 1 except for manufacturing.

About the obtained liquid crystal display device, Example 1
The pulse width range and surface condition were measured by the same method as in. The results are shown in Table 2.

Comparative Example 1 By changing the rubbing direction of the alignment film, the rubbing directions of the alignment films of the two glass substrates with electrodes are the same, that is, the angle at which the rubbing directions intersect (that is, the angle shown in FIG. 2). A liquid crystal display element was manufactured in the same manner as in Example 1 except that a cell in which α) was 0 degrees was manufactured.

About the obtained liquid crystal display device, Example 1
The pulse width range and surface condition were measured by the same method as in. The results are shown in Table 2.

Comparative Example 2 A cell in which the rubbing direction of the alignment film is changed and the angle at which the rubbing directions of the alignment films of the two glass substrates with electrodes intersect (that is, the angle α shown in FIG. 2) is 2 degrees. A liquid crystal display device was manufactured in the same manner as in Example 1 except for manufacturing.

About the obtained liquid crystal display element, Example 1
The pulse width range and surface condition were measured by the same method as in. The results are shown in Table 2.

Comparative Example 3 A cell in which the rubbing direction of the alignment film is changed and the angle at which the rubbing directions of the alignment films of the two glass substrates with electrodes intersect (that is, the angle α shown in FIG. 2) is 40 degrees. A liquid crystal display device was manufactured in the same manner as in Example 1 except for manufacturing.

About the obtained liquid crystal display element, Example 1
The pulse width range and surface condition were measured by the same method as in. The results are shown in Table 2.

[0058]

[Table 2]

As is clear from the results of Table 2, the liquid crystal display elements obtained in the examples were compared with the liquid crystal display elements having the rubbing direction crossing angle outside the range of the present invention obtained in the comparative example. pulse width range is large, PW _S is fast response speed small, and a liquid crystal display device surface was remarkably superior superior.

[0060]

INDUSTRIAL APPLICABILITY The liquid crystal display device of the present invention has a wide range of pulse width, an excellent surface condition, a large response width, and a remarkably excellent effect while the ferroelectric liquid crystal composition is in a uniform state. It is a thing.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an example of a liquid crystal display element of the present invention.

FIG. 2 is a plan view of an example of a liquid crystal display element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 10, 20 Transparent electrode substrate 11, 21 Transparent substrate 12, 22 Transparent electrode 13, 23 Insulating film 14, 24 Alignment film 30 Ferroelectric liquid crystal composition A, B Rubbing direction α Rubbing direction crossing angle

Claims (1)

Claim: What is claimed is: 1. A transparent electrode is provided on a substrate, and two alignment electrodes are provided on the transparent electrode surface. A liquid crystal display device in which a ferroelectric liquid crystal composition is enclosed in a cell configured by disposing, and liquid crystal molecules are aligned in a uniform state,
A liquid crystal display device, wherein the rubbing directions of the alignment films of the two electrode substrates intersect at an angle within a range of 2 to 30 degrees.